Electroplating process



; Patented Oct. 22, 1940 UNITED STATES PATENT OFFICE nmornorm'rmo raoonss Leon R1 Westbrook, Cleveland Heights, Ohio, as-

signor to E. I. du Pont de Nemours & Company, Wilmington, DcL, a corporation of Delaware No Drawing. Application December 30, 1937,

Serial N0. 182,407

12 Claims. (01. 204-18) 7 7 to their low cost, display many characteristics which cause them to be particularly desirable as protective finishes. Zinc, being higher in the electromotive series, will protect iron or steel against rust even after appreciable areas of the base. metal are exposed, whereas the corrosion of i iron'or steel is accelerated by such metals as copper, nickel, and chromium. Despite their numerous advantages over many commonly used coating materials, electrodeposited zinc coatings have not enjoyed the use they deserve because ordinarily they do not possess and do not retain a pleasing appearance, and, consequently, for many purposes they are not acceptable.

Most of the known methods of electrodepositing zinc result in dark colored or dull plates and, even when the deposits at first are fairly satisfactory, they may soon become dark and discolored. The poor appearance of most electrodeposited zinc coatings has limited their use to protective applications, and those working in the art have, for the most part, turned to other protec- .tive materials when it was desired to produce a finish of pleasing appearance.

The electrodeposition of zinc-has ordinarily been accomplished by the use of either an acidzinc bath or a cyanide-zinc bath. Withneither of these baths has it been possible to obtain satisfactorily smooth and bright deposits, but the acid-zinc bath is more commonly used because it leads to a brighter deposit with a better color than does the cyanide-zinc bath.

While, under favorable conditions, thedeposits obtained from acid-zinc baths are relatively white, they are still none too satisfactory because of their relatively coarse crystalline structure.

Numerous attempts have been made to improve the character of zinc deposits obtained from acid baths, and many addition agents, such as glycerine, dextrin, gum tragacanth, licorice, naphthalene compounds, and aluminum com- 0 pounds have been used in conjunction therewith.

While the use of addition agents improved the character of the deposits to some extent, the results were still none too satisfactory. I

In addition to the fact that acid-zinc baths 55 do not produce satisfactory deposits, there are numerous other disadvantages attendant upon their use. For one thing; acid-zinc baths have very poor throwing power, and it is exceedingly diificult satisfactorily to plate irregularly shaped objects. Another disadvantage of acid-zinc advantageous characteristics.

baths is their' low cathode emciency. As zinc above hydrogen in the electromotive force series of metals, it is theoretically impossible to deposit zinc from acid solutions, but, of course, the rather great over-voltage of hydrogen does permit zinc deposition. Concurrently with the deposition of zinc, however, there is a very considerable evolution of hydrogen.

While the deposits obtained from cyanide-zinc baths are poor in appearance, they have a rela-- tively fine crystalline structure. A few addition agents, such as alum, gum arabic, and fluorides, have been tried in cyanide-zinc baths, but the results obtained were none too satisfactory. Aside from the poor appearance of deposits obtainable therefrom, cyanide-zinc baths have a number of throwing power, and it is therefore possible to deposit a relatively uniform zinc coating on irregularly shaped and recessed'articles. Cyanidezinc baths, moreover, have a relatively high cathode efiiciency which, of course, is very advantageous because the electric current applied to the bath is expended less upon the evolution of hydrogen, and more upon the deposition of zinc.

Despite the advantages of cyanide-zinc baths, they have not been much used by the art because of the poor appearance of zinc deposits obtainable therefrom. Regardless of the disadvantages in operation of acid-zinc baths, they have been favored by those working in the art because of the somewhat better appearing deposits obtainable by their use.

A number of proposals. have recently been made for improved methods of electrodepositimg zinc. The art has been enabled, using cyanidezinc baths, to produce relatively smooth and bright zinc plates. Such zinc plates, however, require treatment in a bright-dip, such as dilute nitric acid, before they are entirely satisfactory for some purposes. Those working in the art are frequently desirous of producing as even and bright a finish as possible, and, by using a brightdip, a zinc plate may be made brighter and more uniform in appearance. The deposits, after bright-dipping, also display greater resistance to tarnishing and staining.

The use of a bright-dip is illogical and uneconomieal. The bright-dip removes some of the zinc, and it is wasteful of time, materials, and labor to apply a zinc coating and then remove part of it. The bright-dip treatment, moreover, involves considerable expense for bright-dipping materials and labor. The zinc should be deposited, therefore, in as bright a condition as possible so that a bright-dip treatment would be used, if at all, only when it is desired to produce extremely bright finishes.

I have found that much brighter deposits than those customarily produced can be made with cy- They have good amide-zinc electroplating baths which contain an organic addition agent having a methylenedioxyphenyl group. A metal brightener may be used with the methylenedioxyphenyl compounds of my invention and the metal brightener and organic addition agent cooperate to produce remarkably good results.

The deposits produced from cyanide-zinc plating baths of my invention are of improved character by reason of the inclusion of methylenedioxyphenyl compounds in the bath, and the deposits produced according to the preferred procedures of my invention are brilliant and reflect images with mirror-like fidelity when deposited on polished surfaces. These brilliant deposits are so smooth and bright and are of such a character that bright-dipping them produces no change of any consequence in their appearance and bright-dipping of such deposits particularly when they are on surfaces of a commercial character effects no discernible brightening of the deposit.

The baths of this invention have great throwing power and extremely wide bright current density ranges and. unlike the baths of the prior art, they produce uniform zinc coatings even on recessed articles. to use bright-dips for the purpose of making the coatings uniform. Also, by reasonof the wide bright current density range displayed by cyanide-zinc baths of this invention, it is possible to plate atmuch higher current densities than have heretofore been feasible.

This invention, in its broader aspects, includes some baths containing methylenedioxyphenyl compounds which baths do not produce deposits of extreme brilliance. The methylenedioxyphenyl compounds, nonetheless, eil'ect a distinct improvement in the character of the bath, and often are of particular value in conjunction with metal brighteners.

As is set forth in my co-pending application Serial Number 14,589, filed April 4, 1935, a number of metals may advantageously be used to produce deposits of great smoothness and brightness. These metals appear to exercise some synergetic action in conjunction with organic addition agents, and this action is particularly noticeable when the metals are used in conjunction with methylenedioxyphenyl compounds. Most of the methylenedioxyphenyl compounds seem to have only a small effect when used in cyanide-zinc baths in the absence of a brightening metal, particularly at the higher current densities. It will be particularly observed that methylenedioxyphenyl compounds may advantageously be used alone as organic addition agents without metal brighteners, particularly in baths which are to be used at low current densities.

The organic addition agents of'my invention are oxyheterocyclic compounds characterized by the presence of a methylenedioxyphenyl group, typical members of this class being, for instance, piperonal, piperonyl alcohol, and safrole. It is believed that it is the presence of the oxyheterocyclic ring which makes the compounds of this invention suitable for use as organic addi tion agents in cyanide-zinc plating baths, and it is further believed that the specific presence of a methylenedioxyphenyl group makes the compound of particularly great-eflicacy and value.

The methylenedioxyphenyl compounds employed as addition agents according to my invention should be relatively stable in the bath.

It is therefore unnecessary" that is, they should not lose their oxyheterocyclic form upon contact with a. cyanide-zinc plating solution. The compounds, moreover, should be at least slightly soluble in a cyanide plating bath.

The methylenedioxyphenyl addition agents may be added to a plating bath in a number of ways. The compounds may simply be dumped into the solution and stirred until an adequate amount is dissolved to benefit the bath. It will frequently be found more feasible to fill cloth bags with the addition agent and let these hang suspended in the bath during plating operations. This method is of course particularly efllcacious if the addition agent is best used at the limit of its solubility.

If a methylenedioxyphenyl addition agent is added directly to the plating bath, solution should be expedited by thorough agitation and by raising the temperature of the bath. The temperature of the bath should preferably be raised to a point above the melting point of the methylenedioxyphenyl addition agent. With piperonal, for instance, the bath should be raised to the temperature of 95 F. or higher in which event li-ttle difllculty is experienced in effecting complete dispersion of the required amount of piperonal.

A methylenedioxyphenyl group may also be,

added to a bath advantageously in a suitable solvent. Piperonal, for instance, may be dissolved in methyl or ethyl alcohol and the resulting liquid at a temperature above about F. is then added to the plating bath.

Piperonal forms a sodium bisulfite addition compound and in this form this methylenedioxyphenyl addition agentis most readily added to a plating bath.

this invention, their method of addition to plating baths, and their use alone or in conjunction with brightening metals in accordance with this I invention will be discussed in greater detail in the examples given hereinafter.

The brightening metalsto be used in conjunction with methylenedioxyphenyl compounds according to this invention include aluminum, titanium, and metals found in sub-group. 1 of groups VI and VII, and in group VIII series 4 of Mendelejefls periodic arrangement of the elements. Most of these metals themselves exercise a profound effect upon the character of zinc electrodeposlts obtained from cyanide-zinc plating baths, and, when used with methylenedioxyphenyl compounds, they cause the formation of zinc deposits of great brilliancean'd beauty.

Molybdenum is by far the most satisfactory of the brightening metals for use with methyl-; enedioxyphenyl compounds, the deposits "obtainable by the use of such a combination being markedly superior to those obtainable with most other combinations disclosed herein.

The brightening metals, molybdenum, chromium, tungsten, and uranium found in group VI sub-group 1, may be added to a cyanide-zinc bath in the form of a molybdate, ehromate, tungstate, or uranate of sodium or potassium, or other such compounds which are soluble in the bath.

of a zinc electrodeposit when used alone.but,'iri 7 common with the other brightening metals, they exercise a synergetic action with oxyheterocyclic compounds. The metals of group VIII series 4 are also advantageously employed by reason of their effect upon the metals of'sub-group 1 of groups VI and VII. These metals may be added to the bath in the form of such alkali or cyanidesoluble compounds as potassium ferrocyanide, cobalt sulfate, nickel sulfate, cobalt oxide, and nickel oxide.

A methylenedioxyphenyl compound with or without a brightening metal is employed according to my invention in a cyanide-zinc bath,,numerous examples of which will be given hereinafter. While the cyanide-zinc baths shown herein are typical, it will be understood that the principles of my invention are applicable to any cyanide-zinc plating bath. To obtain the best results it is desirable that the cyanide-zinc plating bath be as pure as possible, and it is particularly important that lead compounds be absent.

- Zinc deposits are ordinarily examined visually and described loosely as rough, treed, smooth, or bright. These inexact designations are differently used by different observers, and it is virtually impossible to compare zinc deposits obtained at different times or made by different individuals.

So that electrodeposited zinc coatings could be more accurately described, an instrument was designed to measure the amountof light reflected by the coatings. This refiectometer, shown and described in detail in British Patent 499,791 is similar to instruments heretofore used for the study of enameled surfaces, paint films, and the like.

The refiectometer includes a light source the light from which is directed through a slit to be reflected from a specimen plate and then to'pass to a photoelectric cell. The photoelectric cell is connected to a microammeter and the reading of the microammeter is taken directly as a measure of comparative brightness. A silver mirror gave a reading of 49 and a less changeable secondary standard, namely a glass mirror, gave a reading of 45 and this standard was used to recheck the instrument from time to time.

In the following examples, unless otherwise stated, specimens were plated on polished copper sheets at current densities from five to one hundred and fifty amperes per square foot. Specimens plated at current densities of about seven, twenty-five, forty, and eighty amperes per square foot were placed on the refiectometer for brightness determinations.

So that the results would be comparable, thedeposits were made on copper plates polished so that on the refiectometer, readings of 30 to 35 would be obtained over the whole surface. When plates differing as much as microamperes were zinc plated under the same conditions and from the same bath, the zinc deposits differed by only about one microampere or less.

While most commercial zinc plating is not done on polished surfaces, the deposits obtained on polished copper sheets are nonetheless significant. A- bath which produces adull deposit on a polished surface will produce a dull and poor deposit on a matte surface, while a bath which produces a bright deposit on a polished surface will produce a correspondingly better deposit on a matte surface. The deposits obtained on polished sheets are therefore valuable in indicating which of a number of baths would lead to the dipping the articles did not visually appear in' brightest deposits when applied to ordinary commercial work.

In the following examples, unless otherwise stated, a cyanide-zinc bath of the following composition was used. 5

, Grams per liter Zinc cyanide (Zn(CN)z) 60 Sodium hydroxide (NaOH) 78 Sodium cyanide (NaCN) 42 At the time the bath was made up, two and flvetenths grams per liter of zinc dust was added together with the bath constituents. The zinc dust effected a removal of deleterious'impurities from the bath.

In the following examples the effect of a bright-dip was observed by subjecting the deposits to the action of a one-fourth per cent solution of nitric acid for about fifteen seconds.

Example 1 Grains per liter Molybdenum trioxide (M003) 8.0 Piperonal 3.5

Zinc was deposited on a number of polished copper sheets, and brightness determined on the re- 35 flectometer according to the above discussed methods.- The results at-the current densities indicated were as follows:

Current density 40 (amps. per sq. ft.) '1 4o 80 Not bright-dipped 33 38 38- Bright-dipped -a 37 38 40 36 The deposits were extremely brilliant and they 43 reflected images with mirror-like fidelity when visually observed. While the refiectometer shows a considerable difierence between bright-dipped and unbright-dipped plates, it is noted that when zinc plated sheets were bright-dipped for about one-half of their area, very little difierence could be observed visually. In some instances it was possible to discern'a line where the bright-dipped and unbright-dipped portions met, but on several deposits no such line could be distinguished.

' A plate, part of which had been bright-dipped, was subjected to a corrosive atmosphere which ordinarily tarnishes unbright-dipped platings in a few hours, and after six days the unbrightdipped portion appeared as bright as the portion which had been bright-dipped.

A large number of commercial steel'articles of various kinds were plated in various types of installations. .All of the zinc deposits were of excellent character and uniformity, and brightany way to improve the appearance or tarnishresistance of the deposits.

The cyanide-zinc-plating bath of this example displayed excellent throwing power and a. wide I bright current density range which extended as high as tests were made, one hundred and fifty amperes per square foot.

Piperonal may be used in widely varying concentrations, tho it is preferably used at about the limit of its solubility in the bath. Much smaller amounts may be employed with good results. At one gram per liter, for instance, the results were not substantially different from those obtained with the bath given above.

The cyanide-zinc plating bath used as standard in this application was made up without the use of addition agents, and a number of deposits made therewith. The following brightness readings were obtained:

Current density (amps. per sq.

Not bright-dipped 15 15 4 '7 Bright-dipped 30 19 17 A cyanide-zinc plating bath was made up using three grams per liter of piperonal. This bath, unlike the one described above did not include a metal brightener. Zinc electrodeposits obtained on polished copper sheets and using this bath gave the following brilliance readings:

Current density (amps. per sq.

Not bright-dipped 25 11 8 10 Bright-dipped 36 29 2'7 26 Piperonal alone as used in this bath effects a rather great improvement in the character of deposits, particularly at low current densities though the deposits before bright-dipping are still somewhat dull particularly at higher current densities. This bath has been used with great success in commercial barrel plating type of Current density (amps. per sq.

Not bright-dipped 15 22 30 30 Bright-dipped 28 30 33 30 It will be apparent that the use of a combination of piperonal and molybdenum results in zinc deposits of great brightness and uniformity particularly at high current densities, and I believe that there is a synergetic action between the organic addition agent and the metal brightener, each being influenced by the other, and both cooperating to produce deposits of excellent character.

The piperonal used in the above baths is very conveniently added as a bisulflte addition compound. This may readily be dissolved in a small amount of warm water and the solution may then be added to a plating bath.

A piperonal-sodium bisulflte addition compound was prepared by slowly adding fifty-five pounds df-piperonal in melted form to an aqueous solution containing 43.5 pounds of sodium bisulfite in one hundred seven pounds (thirteen gallons) of water. The mixture was filtered to separate the addition compound from the liquor and the precipitated addition compound was dried at a temperature of 65 C. The mother liquor was returned as a solvent for more sodium bisulflte.

Example 2 A cyanide-zinc plating bath was made up using piperonal with another brightening metal. To the standard cyanide-zinc bath above given. there was added:

Grams per liter Chromium sulfate (Cr2(SO4)a.15I-Ii0) 4.0 Piperonal 3.5

A number of zinc deposits were produced using this bath, and the following reflectometer readings obtained:

Current density 7 25 40 80 Not bright-dipped 34 34 32 30 Brightdipped 38 34 31 30 The deposits obtained had a very excellent and brilliant appearance, and to the eye they appeared even brighter than the deposits obtained Current density 7 25 40 80 Not bright-dipped 19 19 24 23 Bright-dipped 24 v 24 25 20 Example 3 A cyanide-zinc bath employing two metal brighteners in addition to methylenedioxyphenyl compound was made up as follows:

Grams per liter Zinc oxide (ZnO) 45 Sodium hydroxide (NaOH) 38 Sodium cyanide (NaCN) 100 Molydbenum trioxide (M003) 3 Manganese-cyanide 2.5 Piperonal 3.5

The bath was made up with very pure zinc oxide, sodium hydroxide, and sodium cyanide, and electrolytic zinc anodes were employed to avoid the introduction of deleterious impurities into the bath.

The manganese was added to the bath in the form of a manganese-cyanide complex which was prepared by precipitating it from a water'solution of manganese sulfate by the addition of a water solution of sodium cyanide. of manganese-cyanide used is equivalent to about twenty-five hundredths of a gram per liter of manganese. The molybdenum trioxide used corresponds to about two grams per liter of molybdenum.

Excellent results were obtained using this bath. The zinc deposits were very bright, particularly after bright-dipping. The reflectometer readings taken on specimens made at the indicated current densities were as follows:

Current density 7 25 40 80 Not bright-dipped 36 36 32 Bright-dipped 41 39 33 Example 4 A cyanide-zinc plating bath employing a combination of metalsof group VI sub-group 1, group The amount VIII sub-group 1, and group vm series 4 was Current density '7 25 40 80 made up as Not bright-dipped 29 30 1o '2 Grams per liter Bright-dipped 40 34 18 6 zinc (ZnO) It is noted that the deposits were somewhat 5 Sodium hydroxide (NaOH) -1 38 Sodium cyanide (NaCN) 100 Manganese-cyanide 10 Potassium ierrocyanide (K4Fe(CN) s3H2O) 5 Molybdenum trioxide (M009) 4 Piperonal- 2 3 Zinc deposits made from the bath of this example were of about the same appearance regardless of current density. Irregularly shaped objects, accordingly, were given a coating of very uniform appearance by the use of this bath. The reflectometer readings were as follows:

Current density '7 25 40 80 Not bright-dipped 33 35 35 35 Bright-dipped 38 38 38 38 Example 5 A cyanide-zinc bath employing a metal of group VIII series 4 as well as methylenedioxyphenyl compound was made up with:

Grams per lite Cobalt sulfate (COSO4.7H20) 8 Piperonal 3.5

At current densities up to about forty amperes per square foot very good results were obtained using this bath. The reflectometer readings at the current densities indicated were:

Current density '1 25 4 0 80 Not bright-dipped. 34 32 '1' 12 Bright-dipped s9 37 15 24 this bath were:

Current density '7 25 40 80 Not bright-dipped 23 23 '7- Bright-dipped 24 33 34 23 Example 6 A cyanide-zinc bath employing a metallic brightening agent from group VlI sub-group 1 in conjunction with a methylenedioxyphenyl compound was made up as follows:

Grams per liter Zinc oxide (ZnO) 45 Sodium hydroxide (NaOH) 38 Sodium cyanide (NaCN) 100 Manganese sulfate '(MnSO4.4H2O) 1 Piperonal--- 3.5

The manganese sulfate corresponds to about twenty-five hundredths of a gram per liter of manganese. Both the piperonal and the manganese sulfate were used in aboutthe maximum amount soluble in the bath. More manganese sulfate'was added to the bath in various tests without appreciably different results being obtained. Excellent results were obtained using the bath of this example, and the following reflectometer readings were noted:

cloudy before bright-dipping, therefore causing the reflectometer readings to be rather unexpectedly low. After bright-dipping, however, the deposits were quite brilliant and of very good character.

To observe the effect of the metal brightener apart from the organic addition, a bath was made up as above but omitting the piperonal. The reflectometer readings on plates made with this bath were: Current density 'l 25 40 80 Not bright-dipped 16 13 '3 2 Bright-dipped 31 27 5 2 Example 7 A cyanide-zinc bathusing another metal of group VIII series 4 in conjunction with piperonal. was made up with:

Grams per liter Nickel sulfate (NiSO4.7H20) 0.5 Piperonal 3.5

Using this bath, some deposits of pleasing appearance were obtained. The deposits were somewhat white in color and probably for this reason the reflectometer readings were not as high as one would expect from visual examination. The reflectometer: readings were as follows:

Current density 'z 25 40 9o Not bright-dipped so 29 so 12 Bright-dipped 31 28 2'7 12 Current density '1 25 40 so Not bright-dipped 31 1o- 24 23 Bright-dipped 29 16 22 24 5o I Examples A cyanide-zinc bath was made up with:

. Grams per liter Potassium ferrocyanide (K4Fe(CN)e3H-.1O) 12 Piperonal. 3.5

Zinc deposits obtained usingthis bath had a brownish film. Reflectometer readings wereobtained as follows: Current density 7 25 40 80 Not bright-dipped. 23 14 14 14 Bright-dipped 37 35 35 35 It will be observed that bright-dipping the plates removed the film arid led to the production of very satisfactory deposits.

To observe the effect of the metal brightener apart from the organic addition, a bath was made up as above omitting the piperonal. The reflectometer readings on plates made with this bath.

were:

Current-density '7 25 40 Not. bright-di ed- 13 12 9 9 Bright-dipped 23 2'1 26 2'1 5 Example 9 A cyanide-zinc plating bath was made up with:

Grams per liter Titanyl sulfate (TiOSOt) 0.5 Piperonal 3.5

Employing this bath, specimens were obtained with the following reflectometer readings:

Current density 7 40 80 Not bright-dipped 27 24 13 7 Bright-dipped 34 32 28 These deposits were dull by reason of a film thereon which bright-dipping removed.

To observe the eflect of the metal brightener apart from the organic addition, a bath was made up as above but omitting the piperonal. The refiectometer readings on plates made with this bath were:

Current density 7 25 40 so Not bright-dipped 16 n 14 11 13 Bright-dipped 33 2a 25 2'2 Example 10 A cyanide-zinc plating bath was made up with:

Grams per liter Potassium perrhenate (KReO4) 0.1 Piperonalnu, 3.5

Deposits produced at the indicated current densities gave the following refiectometer readings:

Current density 7 25 40 80 Not bright-dipped 22 21 27 24 Bright-dipped 32 29 36 To observe the effect of the metal brightener apart from the organic addition, a bath was made up as above but omitting the piperonal. The reflectometer readings on plates made with this bath were:

Current density 7 25 80 Not bright-dipped 24 24 22 5 Bright-dipped 30 23 27 14 Example 11 A cyanide-zinc plating bath was made up as follows:

Grams per liter Zinc oxide (ZnO) Sodium hydroxide (NaOH) 38 Sodium cyanide (NaCN) 1 100 Tungsten trioxide (W01) 8 Piperonal 3.5

The tungsten trioxide used corresponds to about six and four-tenths grams per liter of tungsten. Specimen plates were made up at the below indicated current densities with the following results:

Current density '7 25 40 80 Not' bright-dipped 32 33 13 4 Bright-dipped -1 38 36 17 8 To observe the effect of the metal brightener apart from the organic addition, a bath was made up as above omitting the piperonal. The reflectometer readings on plates made with this bath were: 2

Current density v 7 25 40 so not bright-dipped 12 23 a 1 Bright-dipped 31 2a 9 1 anemic Example 12 Another oxyheterocyclic compound winch may advantageously be employed is piperonylic acid. This compound, also known as methylene-protocatechuic acid, may be regarded as a derivative of piperonal. Like piperonal, piperonylicacid is characterized by the presence of the methylenedioxyphenyl group. A cyanide-zinc plating bath was made up with:

Grams per liter Molybdic aci 8 Piperonylic acid 4 The piperonylic acid went into solution rather readily. A number of polished copper sheets were zinc plated using this bath, and the following reflectometer readings were obtained at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 17 36 36 29 Bright-dipped 33 4O 37 30 A cyanide-zinc plating bath was also made up as above using piperonylic acid but omitting the molybdic acid. When not using the metal brightener, the following results were obtained:

The deposits obtained using this bath were of very good character though the reflectometer readings were somewhat low before bright-dipping. The deposits obtained at the indicated current densities gave the following results:

Current density 7 25 40 80 Not bright-dipped 24 21 23 23 Bright-dipped 41 35 34 32 A cyanide-zinc plating bath was made up as above but omitting the organic addition agent piperonylic acid. With aluminum thus used as a metal brightener, the following results were obtained:

Current density '7 25 40 80 Not bright-dipped e e 3 2 Bright-dipped 14 16 11 'l Example 14 A cyanide-zinc plating bath was made up with:

Grams per liter Chromium sulfate (Cra(SO4)a.15H:O) 4

Piperonylic acid 4 Employing this bath, the following results were obtained:

Current density 7 25 40 80 Not bright-dipped as 3s 2s 24 Bright-dipped 36 32 28 26 Example 15 A cyanide-zinc plating bath was made up with:

Grams per liter Cobalt sulfate (COSO4.7H20) 8 Piperonylic acid 4 Zinc deposits obtained from this bath gave the following results:

Current density"; 7 25 40 8t) Not bright-dipped z.. 22 33 29 14 Bright-dipped 34 3,7 37 21 Example 16 Grams per liter Molybdenum trioxide (MoOaL 8 a Piperine 1 It is observed that even less than the one gram per liter of the piperine seemed to be dissolved in the solution. After one plate was made using this bath, a white flocculent precipitate appeared.

Zinc deposits made On polished copper sheets and using the bath of this example gave the following reflectometer readings at the indicated current densities:

'0 Current density 7 25 40 80 Not bright-dipped 1'1 22 27 24 Bright-dipped 32 32 30 26 a bath similar to that of this example was made up using piperine but omitting molybdenum. The

a following results were obtained:

Current density 'l 25 40 80v Not bright-dipped 1'1 7 7 6 Bright-dipped 32 21 21 18 Example 17 v A cyanide-zinc bath was made up with:

Grams per liter Chromium sulfate (Cr(SO4)a.15HaO) 4 ll Piperine 1 Using this bath, the following results were obtained:

60 Plates made using this bath were quite satisfactory without bright-dipping and, as is usualwith deposits made employing nickel, bright-dipping was not advantageous. The reflectometer readings at the current densities indicated were as .5 follows:

Current density '7 25 40 80 Not bright-dipped 35 36 34 23 Bright-dipped 35 33 28 70 Example 19 A cyanide-zinc plating bath was made up with:

Grams per liter Cobalt sulfate (CoSOa'lI-IaO) 8 15 Piperine 1 Employing this bath the following results were obtained:

Current density....' ]'l 25* 40 so Not bright-dipped 17 27 25 17 5 Bright-dipped 28 35 31 23 Example Safrole, the oxyheterocyclic compound from which piperonal is commercially derived, is also 10 characterized-by the presence of a methylenedioxyphenyl group. Safrole is quite insoluble in water, and even adding it to the bath in alcohol solution does not greatly increase the amount of safrole which can be dissolved. Despite the al- 1 most negligible solubility of this compound, baths employing it show a very considerable improvement. Employing this oxyheterocyclic compound and applicants preferred metal brightener, a cyanide-zinc plating bath was made up with: 20

' Grams per liter Molybdenum trioxide (M002) 8 Safrole 1 Deposits of good appearance were obtained using this bath. The reflectometer readings were as follows at the indicated current densities:

Current density 7 25 40 80 Not bright-dipped 13 25 28 2'7 Bright-dipped 27 34 35 34 A bath was also made up using safrole but. omitting the molybdenum. With this bath the following results were obtained:

35- Current density 7 25 80 Not bright-dipped 12 10 9 8 Bright-dipped 30 29 28 28 Example 21 40 A cyanide-zinc bath wasmade up with:

Grams per liter Chromium sulfate (Cr(SO4):.15H-.-O) 4 Safrole 1 Employing this bath, the following results were obtained:'

Current density "l 25 40 80 Not bright-dipped 21 2a 23 22 Bright-dipped 28 29 29 32 Example 22 A cyanide-zinc plating bath was made up with:

Grams per liter Cobalt sulfate (C0SO4.7H2O) 8 Safrole 1 The following reflectometer readings were obtained at the indicated current densities:

Current density 'l 25 40 80 Not bright-dipped 15 23 27 20 Bright-dipped"; 26 31 31 31 Example 23 Another oxyheterocyclic compound characterized by the presence of the methylenedioxyphenyl group is piperonyl alcohol. This compound was employed together with a metal brightener in a cyanide-zinc plating bath made up including:

3 Grams per liter Molybdenum trioxide (MoOa) 8 Piperonyl alcohol 5 Good results were obtained using this bath and at a current density of about forty amperes per square foot reflectometer readings of thiigty-one were obtained on unbright-dipped plates, "and of a thirty-five on bright-dipped plates. J

A bath was also made up employing piperonyl alcohol but omitting the molybdenum. This bath was improved slightly by the use of the piperonyl alcohol, the following refiectometer readings be- The piperonal acetophenone was quite insoluble, tho the small amount which dissolved effected 3o considerable improvement. Employing this bath the following reflectometer readings were obtained at the indicated current densities:

Currentdensity 7 40 so Not bright-dipped 16 29 34' 28 Bright-dipped 33' as 35 31 A similar cyanide-zinc bath was made up employing piperonal acetophenone but omitting molybdenum. The following results were obtained:

Current density 7 25 40 80 Not bright-dipped 15 23 25- 21 Bright-dipped 28 30 33 33,

While, in the foregoing examples, the brightening metals are employed in about the optimum amounts for the particular baths shown, the quantities used may be greatly varied. Generally, the metals must be used in substantial amount to have a satisfactorily cooperative effect.

It will readily be understood that the optimum amount of the various metals will depend upon the particular bath used, upon the organic addition agent used, and upon whether or not the metals are used in combination with "other brightening metals. The-best proportion of bath constituentsmay readily be determined for each particular instance by a few trials.

The metals of group VI sub-group 1 may be used in widely varying amounts, the upper limit on the quantity being largely determined by economic considerations. In view of the high cost of the metals of this group, it wouldnot at the present time be commercially feasible to employ them in large quantities. More specifically, the metals of group VI sub-group 1 should be used in amounts not substantially less than about one hundredth of a gram per liter, and no more than about forty grams per liter can economically be used.

Molybdenum is the best metal of this group and it is, in fact, by far the best of the brightening metals. I generally prefer to use from about twenty-five hundredths of a gram to twenty-five grams per liter of molybdenum. More specifically, it is preferred to use from aboutone to twelve grams per liter of molybdenum. It will be understood that while reference is made to the amount of metal used, the metal is present in the 5 bath in the form of a soluble compound.

The metals of group VII sub-group 1 should also be employed in substantial amounts. It is generally desirable to use no less than about five-thousandths of a gram per liter and not sub- 10 stantially more than about fifteen grams per liter. Manganese is preferably used in amounts between about one and five grams per liter, while, more specifically, about one to three grams per liter should be used.

The metals of group VIII series 4, similarly, should be used in substantial amounts as soluble compounds such as potassium ferrocyanide, cobalt sulfate, cobalt chloride, cobalt oxide, nickel sulfate, nickel chloride, and nickel oxide. Generally a soluble compound equivalent to no less than about five-hundredths of a gram per liter of one of these metals should be used.

When titanium is employed as a brightening metal, an amount equivalent to about one-half gram per liter of titanyl sulfate should be used,- tho, of course, larger or smaller amounts may be employed if desired.

While the amount of aluminum used as a bright- 30 ening metal may be greatly varied, it is generally desirable to employ an amount of aluminum equivalent to about five to twelve grams per liter of aluminum sulfate.

While an attempt has been made above to outline, roughly, some of the considerations involved in selecting the quantities of metal brighteners, it will be understood that in a particular instance the requirements may most readily be determined by a few simple trials.

Each of the brightening metals has character istics peculiar toitself, and the selection of a metal brightener for a particular bath may be influenced by the characteristics desired. While, generally speaking, I may employ any metal brightener in'conjunction with organic addition 45 agents, it is preferred to use a metal from the group consisting of molybdenum, chromium,'cobalt, manganese, nickel, iron, titanium, rhenium, aluminum, and tungsten.

Molybdenum is by far the best of the brightening metals as has been pointed out above, tho occasionally some otherbrightening metal will give comparableresultsin a particular combination.

Chromium is very satisfactory as a brightening metal, but it has the fault of hydrolyzing in the bath and precipitating out. This characteristic of chromium brighteners makes their use too expensive for most purposes. 60

Cobalt and nickel both have the fault of accelerating anode corrosion tho nickel is a much worse offender than cobalt. When cobalt is used as a metal brightener the deposits appear a little white, and the reflectometer readings are lower 05 than one would expect from visual observation. In many combinations nickel produces quite satisfactory deposits but the deposits should not be bright-dipped. Deposits produced from baths containing nickel as a brightener darken when To bright-dipped tho they still appear bright to the eye.

When manganese or tungsten are used as brightening metals, the deposits have a brownish film. Despite the fact that many deposits of pleas- 7s I saunas 9 'ingandbrilllantappearanccareobtainedusing these metals, the deposits almost llfluol'mly give much lower reflectometer readings than would be expected from visual observation. The brownish 5 film is removed when the deposits are brighta slight gray film which greatly lowers the rell flectometer readings. The gray film is not ordinarily removed by bright-dipping the deposit.

when aluminum is used as a metal brightener the deposits ordinarily have a whitish appearance, and while the deposits are very pleasing and N bright when visually observed, the reilectometer readings are astonishingly low. Bright-dipping does not entirely change the whitish appearance oi the deposit.

Rhenium is quite excellent as a brightening 28 metal, but it is so rare at the present time that its commercial application would be impractical. Should the metal become less expensive, it could be used very satisfactorily as a brightener.

While I may employ any methylenedioxyphenyl compound with or without a metal brightener, it is preferred to employ a methylenedioxyphenyl compound from the group consisting of piperonal,

piperonyl alcohol, piperonylic acid, piperine,

sai'role, and piperonal acetophenone.

The methylenedioxyphenyl compounds are preferably employed in about the amounts given in the above examples. Itwill be understood that the quantity used in the examples was determined in each instance by trying the organic so addition agent at widely varying concentrations until about an optimum was found. If it is desired to employ a particular oxyheterocycllc compound in a still different specific instance, the amount to be used may readily be' determined by as a few simple tests. I x;

' While I have shown a number of specifi proccases and cyanide-zinc baths in the foreg ing, it will be understood that I do not intend to be limited thereto. Those skilled in the art may l0 readily make numerous modifications of the dis- .cussed processes and baths without departin from the spirit of this invention.

This application is a continuation in part of my application Serial Number 14,589, filed April ll 4, 1935, and of my application Serial Number 10,400, iiled March 23. 1936, and is a division-inpartoi my co-pendlng application Serial Number 98,455, tiled August 29, 1936.

I claim:

1. In a process for the electrodeposition of zinc,

m a process for the electrodeposition oi sine. the step comprisinghdepositing' zinc irom a mnide-ainc bath in the presence oi a compound containing a methylenedioxyphenyl group and in the presence of a soluble compound of a metal 5 of the group consisting of molybdenum, chromium, cobalt, manganese, nickel. iron, titanium,

rhenium, aluminum,and tungsten.

3. In a process for the electrodeposition oi zinc, the step comprising depositing zinc from a cy'al0 nide-zinc bath in the presence of an oxyheterocyclic compound selected from the group consisting of piperonal, piperonyl alcohol, piperonylic acid, piperine, sairole, and piperonal acetophenone. 1

4. In a process for the electrodepositlon of zinc,

the step comprising depositing zinc from a cyanide-zinc bath in the presence of an oxyheterocycllc compound selected from the group consisting of piperonal, plperonyl alcohol, piperonylic acid, 20

piperine, safrole, and piperonal acetophenone and ing a compound containing a methylenedioxya phenyl roup- 8. A cyanide-zinc plating composition containing a compound containing a methylenedioxyphenyl group and in the presence of a soluble compound of a metal of the group consisting of molybdenum, chromium, cobalt, manganese, w nickel, iron, titanium, rhenium, aluminum. and

tungsten.

the group consisting of piperonal, piperonyl alcoa hol, piperonylic acid, piperine, sairole, and piperonal acetophenone and in the presence of a soluble compound of a metal of the group consisting oi molybdenum, chromium, cobalt, manganese, nickel, iron, titanium, rhenium, aluminum, and tungsten.

ii. A cyanide-sine plating composition containing piperonal. I

12. A cyanide-zinc plating composition containing piperonal and a soluble molybdenum compound.

LEON R. K. 

